Method and system for accessing a file

ABSTRACT

A method for accessing a file in a storage system is provided. The method includes determining, for each file chunk of the file, an authority among differing storage nodes of the storage system and receiving from the authority having ownership of the file chunk, location information for the file chunk. The method includes accessing file chunks of the file as directed by each of the determined authorities.

BACKGROUND

Solid-state memory, such as flash, is currently in use in solid-statedrives (SSD) to augment or replace conventional hard disk drives (HDD),writable CD (compact disk) or writable DVD (digital versatile disk)drives, collectively known as spinning media, and tape drives, forstorage of large amounts of data. Flash and other solid-state memorieshave characteristics that differ from spinning media. Yet, manysolid-state drives are designed to conform to hard disk drive standardsfor compatibility reasons, which makes it difficult to provide enhancedfeatures or take advantage of unique aspects of flash and othersolid-state memory. Large files, such as in the gigabyte range andupwards, place a burden on storage system load, and may tie up resourcesof a storage node thus producing a bottleneck in storage cluster orstorage system performance. It is within this context that theembodiments described herein arise.

SUMMARY

In some embodiments, a method for accessing a file in a storage systemis provided. The method includes determining, for each file chunk of thefile, an authority among differing storage nodes of the storage systemand receiving from the authority having ownership of the file chunk,location information for the file chunk. The method includes accessingfile chunks of the file as directed by each of the determinedauthorities.

In some embodiments, a method for accessing file chunks of a file in astorage system is provided. The method includes determining one of aplurality of owners in a plurality of storage nodes as having ownershipof a file chunk of the file, the determining performed at differingstorage nodes for each of a plurality of file chunks of the file. Themethod includes accessing the plurality of file chunks of the file asdirected by determined owners.

In some embodiments, a storage system having efficient distribution offile chunks is provided. The system includes a plurality of storagenodes coupled as a storage cluster. At least a portion of the pluralityof storage nodes is configured to have at least one authority, eachauthority having ownership of a subset of file chunks, each file chunkincluding a portion of a file. Each of the plurality of storage nodes isconfigured to determine which authority in which of the plurality ofstorage nodes has information regarding location in the storage clusterof each file chunk.

Other aspects and advantages of the embodiments will become apparentfrom the following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments and the advantages thereof may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings. These drawings in no waylimit any changes in form and detail that may be made to the describedembodiments by one skilled in the art without departing from the spiritand scope of the described embodiments.

FIG. 1 is a perspective view of a storage cluster with multiple storagenodes and internal storage coupled to each storage node to providenetwork attached storage, in accordance with some embodiments.

FIG. 2 is a block diagram showing an interconnect switch couplingmultiple storage nodes in accordance with some embodiments.

FIG. 3 is a multiple level block diagram, showing contents of a storagenode and contents of one of the non-volatile solid state storage unitsin accordance with some embodiments.

FIG. 4A depicts a file, suitable for storage and access in embodimentsof the storage cluster, with file chunks each having a file offsetrelative to the file.

FIG. 4B shows an example file, and ownership of various file chunks ofthe file, in accordance with an embodiment of the present description.

FIG. 5 is a block diagram of a storage cluster with components fordetermining ownership of file chunks.

FIG. 6 is a system action diagram showing use of a hash calculator and alookup table to point to an authority as an owner of a file chunk.

FIG. 7A is a flow diagram of a method for distributing ownership of filechunks in a storage system, and writing file chunks of files, which canbe practiced by embodiments of the storage cluster, storage nodes andstorage units of FIGS. 1-6.

FIG. 7B is a flow diagram of a method for distributing ownership of filechunks in a storage system, and reading file chunks of files, which canbe practiced by embodiments of the storage cluster, storage nodes andstorage units of FIGS. 1-6.

FIG. 8 is an illustration showing an exemplary computing device whichmay implement the embodiments described herein.

DETAILED DESCRIPTION

A storage cluster, with storage nodes and storage units that havestorage memory, is herein described as having a mechanism thatdistributes, to multiple storage nodes, information about physicallocation of file chunks of files, rather than concentrating all suchinformation in a single storage node, or all such information about filechunks of each file in a storage node that owns that file. Distributingthe information as metadata to multiple storage nodes leads to efficientdistribution of large files. In various embodiments, storage nodes use ahash calculation, of an inode number of a file and an offset of the filechunk relative to the file, to point via a lookup table to informationabout the physical location of the file chunk, for each file chunk ofthe file. Since neither the performance of the hash calculation nor thelookup table are limited to belonging to only one storage node, thestorage system avoids a bottleneck situation. Embodiments of storageclusters, storage nodes and storage units are described with referenceto FIGS. 1-3. Processes and mechanisms for obtaining information aboutthe physical location of a file chunk, in embodiments of storage nodesand embodiments of a storage system, are described with reference toFIGS. 4A-7B.

The embodiments below describe a storage cluster that stores user data,such as user data originating from one or more user or client systems orother sources external to the storage cluster. The storage clusterdistributes user data across storage nodes housed within a chassis,using erasure coding and redundant copies of metadata. Erasure codingrefers to a method of data protection or reconstruction in which data isstored across a set of different locations, such as disks, storage nodesor geographic locations. Flash memory is one type of solid-state memorythat may be integrated with the embodiments, although the embodimentsmay be extended to other types of solid-state memory or other storagemedium, including non-solid state memory. Control of storage locationsand workloads are distributed across the storage locations in aclustered peer-to-peer system. Tasks such as mediating communicationsbetween the various storage nodes, detecting when a storage node hasbecome unavailable, and balancing I/Os (inputs and outputs) across thevarious storage nodes, are all handled on a distributed basis. Data islaid out or distributed across multiple storage nodes in data fragmentsor stripes that support data recovery in some embodiments. Ownership ofdata can be reassigned within a cluster, independent of input and outputpatterns. This architecture described in more detail below allows astorage node in the cluster to fail, with the system remainingoperational, since the data can be reconstructed from other storagenodes and thus remain available for input and output operations. Invarious embodiments, a storage node may be referred to as a clusternode, a blade, or a server.

The storage cluster is contained within a chassis, i.e., an enclosurehousing one or more storage nodes. A mechanism to provide power to eachstorage node, such as a power distribution bus, and a communicationmechanism, such as a communication bus that enables communicationbetween the storage nodes are included within the chassis. The storagecluster can run as an independent system in one location according tosome embodiments. In one embodiment, a chassis contains at least twoinstances of both the power distribution and the communication bus whichmay be enabled or disabled independently. The internal communication busmay be an Ethernet bus, however, other technologies such as PeripheralComponent Interconnect (PCI) Express, InfiniBand, and others, areequally suitable. The chassis provides a port for an externalcommunication bus for enabling communication between multiple chassis,directly or through a switch, and with client systems. The externalcommunication may use a technology such as Ethernet, InfiniBand, FibreChannel, etc. In some embodiments, the external communication bus usesdifferent communication bus technologies for inter-chassis and clientcommunication. If a switch is deployed within or between chassis, theswitch may act as a translation between multiple protocols ortechnologies. When multiple chassis are connected to define a storagecluster, the storage cluster may be accessed by a client using eitherproprietary interfaces or standard interfaces such as network filesystem (NFS), common internet file system (CIFS), small computer systeminterface (SCSI) or hypertext transfer protocol (HTTP). Translation fromthe client protocol may occur at the switch, chassis externalcommunication bus or within each storage node.

Each storage node may be one or more storage servers and each storageserver is connected to one or more non-volatile solid state memoryunits, which may be referred to as storage units. One embodimentincludes a single storage server in each storage node and between one toeight non-volatile solid state memory units, however this one example isnot meant to be limiting. The storage server may include a processor,dynamic random access memory (DRAM) and interfaces for the internalcommunication bus and power distribution for each of the power buses.Inside the storage node, the interfaces and storage unit share acommunication bus, e.g., PCI Express, in some embodiments. Thenon-volatile solid state memory units may directly access the internalcommunication bus interface through a storage node communication bus, orrequest the storage node to access the bus interface. The non-volatilesolid state memory unit contains an embedded central processing unit(CPU), solid state storage controller, and a quantity of solid statemass storage, e.g., between 2-32 terabytes (TB) in some embodiments. Anembedded volatile storage medium, such as DRAM, and an energy reserveapparatus are included in the non-volatile solid state memory unit. Insome embodiments, the energy reserve apparatus is a capacitor,super-capacitor, or battery that enables transferring a subset of DRAMcontents to a stable storage medium in the case of power loss. In someembodiments, the non-volatile solid state memory unit is constructedwith a storage class memory, such as phase change or magnetoresistiverandom access memory (MRAM) that substitutes for DRAM and enables areduced power hold-up apparatus.

One of many features of the storage nodes and non-volatile solid statestorage is the ability to proactively rebuild data in a storage cluster.The storage nodes and non-volatile solid state storage can determinewhen a storage node or non-volatile solid state storage in the storagecluster is unreachable, independent of whether there is an attempt toread data involving that storage node or non-volatile solid statestorage. The storage nodes and non-volatile solid state storage thencooperate to recover and rebuild the data in at least partially newlocations. This constitutes a proactive rebuild, in that the systemrebuilds data without waiting until the data is needed for a read accessinitiated from a client system employing the storage cluster. These andfurther details of the storage memory and operation thereof arediscussed below.

FIG. 1 is a perspective view of a storage cluster 160, with multiplestorage nodes 150 and internal solid-state memory coupled to eachstorage node to provide network attached storage or storage areanetwork, in accordance with some embodiments. A network attachedstorage, storage area network, or a storage cluster, or other storagememory, could include one or more storage clusters 160, each having oneor more storage nodes 150, in a flexible and reconfigurable arrangementof both the physical components and the amount of storage memoryprovided thereby. The storage cluster 160 is designed to fit in a rack,and one or more racks can be set up and populated as desired for thestorage memory. The storage cluster 160 has a chassis 138 havingmultiple slots 142. It should be appreciated that chassis 138 may bereferred to as a housing, enclosure, or rack unit. In one embodiment,the chassis 138 has fourteen slots 142, although other numbers of slotsare readily devised. For example, some embodiments have four slots,eight slots, sixteen slots, thirty-two slots, or other suitable numberof slots. Each slot 142 can accommodate one storage node 150 in someembodiments. Chassis 138 includes flaps 148 that can be utilized tomount the chassis 138 on a rack. Fans 144 provide air circulation forcooling of the storage nodes 150 and components thereof, although othercooling components could be used, or an embodiment could be devisedwithout cooling components. A switch fabric 146 couples storage nodes150 within chassis 138 together and to a network for communication tothe memory. In an embodiment depicted in FIG. 1, the slots 142 to theleft of the switch fabric 146 and fans 144 are shown occupied by storagenodes 150, while the slots 142 to the right of the switch fabric 146 andfans 144 are empty and available for insertion of storage node 150 forillustrative purposes. This configuration is one example, and one ormore storage nodes 150 could occupy the slots 142 in various furtherarrangements. The storage node arrangements need not be sequential oradjacent in some embodiments. Storage nodes 150 are hot pluggable,meaning that a storage node 150 can be inserted into a slot 142 in thechassis 138, or removed from a slot 142, without stopping or poweringdown the system. Upon insertion or removal of storage node 150 from slot142, the system automatically reconfigures in order to recognize andadapt to the change. Reconfiguration, in some embodiments, includesrestoring redundancy and/or rebalancing data or load.

Each storage node 150 can have multiple components. In the embodimentshown here, the storage node 150 includes a printed circuit board 158populated by a CPU 156, i.e., processor, a memory 154 coupled to the CPU156, and a non-volatile solid state storage 152 coupled to the CPU 156,although other mountings and/or components could be used in furtherembodiments. The memory 154 has instructions which are executed by theCPU 156 and/or data operated on by the CPU 156. As further explainedbelow, the non-volatile solid state storage 152 includes flash or, infurther embodiments, other types of solid-state memory.

Referring to FIG. 1, storage cluster 160 is scalable, meaning thatstorage capacity with non-uniform storage sizes is readily added, asdescribed above. One or more storage nodes 150 can be plugged into orremoved from each chassis and the storage cluster self-configures insome embodiments. Plug-in storage nodes 150, whether installed in achassis as delivered or later added, can have different sizes. Forexample, in one embodiment a storage node 150 can have any multiple of 4TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, astorage node 150 could have any multiple of other storage amounts orcapacities. Storage capacity of each storage node 150 is broadcast, andinfluences decisions of how to stripe the data. For maximum storageefficiency, an embodiment can self-configure as wide as possible in thestripe, subject to a predetermined requirement of continued operationwith loss of up to one, or up to two, non-volatile solid state storageunits 152 or storage nodes 150 within the chassis.

FIG. 2 is a block diagram showing a communications interconnect 170 andpower distribution bus 172 coupling multiple storage nodes 150.Referring back to FIG. 1, the communications interconnect 170 can beincluded in or implemented with the switch fabric 146 in someembodiments. Where multiple storage clusters 160 occupy a rack, thecommunications interconnect 170 can be included in or implemented with atop of rack switch, in some embodiments. As illustrated in FIG. 2,storage cluster 160 is enclosed within a single chassis 138. Externalport 176 is coupled to storage nodes 150 through communicationsinterconnect 170, while external port 174 is coupled directly to astorage node. External power port 178 is coupled to power distributionbus 172. Storage nodes 150 may include varying amounts and differingcapacities of non-volatile solid state storage 152 as described withreference to FIG. 1. In addition, one or more storage nodes 150 may be acompute only storage node as illustrated in FIG. 2. Authorities 168 areimplemented on the non-volatile solid state storages 152, for example aslists or other data structures stored in memory. In some embodiments theauthorities are stored within the non-volatile solid state storage 152and supported by software executing on a controller or other processorof the non-volatile solid state storage 152. In a further embodiment,authorities 168 are implemented on the storage nodes 150, for example aslists or other data structures stored in the memory 154 and supported bysoftware executing on the CPU 156 of the storage node 150. Authorities168 control how and where data is stored in the non-volatile solid statestorages 152 in some embodiments. This control assists in determiningwhich type of erasure coding scheme is applied to the data, and whichstorage nodes 150 have which portions of the data. Each authority 168may be assigned to a non-volatile solid state storage 152. Eachauthority may control a range of inode numbers, segment numbers, orother data identifiers which are assigned to data by a file system, bythe storage nodes 150, or by the non-volatile solid state storage 152,in various embodiments.

Every piece of data, and every piece of metadata, has redundancy in thesystem in some embodiments. In addition, every piece of data and everypiece of metadata has an owner, which may be referred to as anauthority. If that authority is unreachable, for example through failureof a storage node, there is a plan of succession for how to find thatdata or that metadata. In various embodiments, there are redundantcopies of authorities 168. Authorities 168 have a relationship tostorage nodes 150 and non-volatile solid state storage 152 in someembodiments. Each authority 168, covering a range of data segmentnumbers or other identifiers of the data, may be assigned to a specificnon-volatile solid state storage 152. In some embodiments theauthorities 168 for all of such ranges are distributed over thenon-volatile solid state storages 152 of a storage cluster. Each storagenode 150 has a network port that provides access to the non-volatilesolid state storage(s) 152 of that storage node 150. Data can be storedin a segment, which is associated with a segment number and that segmentnumber is an indirection for a configuration of a RAID (redundant arrayof independent disks) stripe in some embodiments. The assignment and useof the authorities 168 thus establishes an indirection to data.Indirection may be referred to as the ability to reference dataindirectly, in this case via an authority 168, in accordance with someembodiments. A segment identifies a set of non-volatile solid statestorage 152 and a local identifier into the set of non-volatile solidstate storage 152 that may contain data. In some embodiments, the localidentifier is an offset into the device and may be reused sequentiallyby multiple segments. In other embodiments the local identifier isunique for a specific segment and never reused. The offsets in thenon-volatile solid state storage 152 are applied to locating data forwriting to or reading from the non-volatile solid state storage 152 (inthe form of a RAID stripe). Data is striped across multiple units ofnon-volatile solid state storage 152, which may include or be differentfrom the non-volatile solid state storage 152 having the authority 168for a particular data segment.

If there is a change in where a particular segment of data is located,e.g., during a data move or a data reconstruction, the authority 168 forthat data segment should be consulted, at that non-volatile solid statestorage 152 or storage node 150 having that authority 168. In order tolocate a particular piece of data, embodiments calculate a hash valuefor a data segment or apply an inode number or a data segment number.The output of this operation points to a non-volatile solid statestorage 152 having the authority 168 for that particular piece of data.In some embodiments there are two stages to this operation. The firststage maps an entity identifier (ID), e.g., a segment number, inodenumber, or directory number to an authority identifier. This mapping mayinclude a calculation such as a hash or a bit mask. The second stage ismapping the authority identifier to a particular non-volatile solidstate storage 152, which may be done through an explicit mapping. Theoperation is repeatable, so that when the calculation is performed, theresult of the calculation repeatably and reliably points to a particularnon-volatile solid state storage 152 having that authority 168. Theoperation may include the set of reachable storage nodes as input. Ifthe set of reachable non-volatile solid state storage units changes theoptimal set changes. In some embodiments, the persisted value is thecurrent assignment (which is always true) and the calculated value isthe target assignment the cluster will attempt to reconfigure towards.This calculation may be used to determine the optimal non-volatile solidstate storage 152 for an authority in the presence of a set ofnon-volatile solid state storage 152 that are reachable and constitutethe same cluster. The calculation also determines an ordered set of peernon-volatile solid state storage 152 that will also record the authorityto non-volatile solid state storage mapping so that the authority may bedetermined even if the assigned non-volatile solid state storage isunreachable. A duplicate or substitute authority 168 may be consulted ifa specific authority 168 is unavailable in some embodiments.

With reference to FIGS. 1 and 2, two of the many tasks of the CPU 156 ona storage node 150 are to break up write data, and reassemble read data.When the system has determined that data is to be written, the authority168 for that data is located as above. When the segment ID for data isalready determined the request to write is forwarded to the non-volatilesolid state storage 152 currently determined to be the host of theauthority 168 determined from the segment. The host CPU 156 of thestorage node 150, on which the non-volatile solid state storage 152 andcorresponding authority 168 reside, then breaks up or shards the dataand transmits the data out to various non-volatile solid state storage152. The transmitted data is written as a data stripe in accordance withan erasure coding scheme. In some embodiments, data is requested to bepulled, and in other embodiments, data is pushed. In reverse, when datais read, the authority 168 for the segment ID containing the data islocated as described above. The host CPU 156 of the storage node 150 onwhich the non-volatile solid state storage 152 and correspondingauthority 168 reside requests the data from the non-volatile solid statestorage and corresponding storage nodes pointed to by the authority. Insome embodiments the data is read from flash storage as a data stripe.The host CPU 156 of storage node 150 then reassembles the read data,correcting any errors (if present) according to the appropriate erasurecoding scheme, and forwards the reassembled data to the network. Infurther embodiments, some or all of these tasks can be handled in thenon-volatile solid state storage 152. In some embodiments, the segmenthost requests the data be sent to storage node 150 by requesting pagesfrom storage and then sending the data to the storage node making theoriginal request.

In some systems, for example in UNIX-style file systems, data is handledwith an index node or inode, which specifies a data structure thatrepresents an object in a file system. The object could be a file or adirectory, for example. Metadata may accompany the object, as attributessuch as permission data and a creation timestamp, among otherattributes. A segment number could be assigned to all or a portion ofsuch an object in a file system. In other systems, data segments arehandled with a segment number assigned elsewhere. For purposes ofdiscussion, the unit of distribution is an entity, and an entity can bea file, a directory or a segment. That is, entities are units of data ormetadata stored by a storage system. Entities are grouped into setscalled authorities. Each authority has an authority owner, which is astorage node that has the exclusive right to update the entities in theauthority. In other words, a storage node contains the authority, andthat the authority, in turn, contains entities.

A segment is a logical container of data in accordance with someembodiments. A segment is an address space between medium address spaceand physical flash locations, i.e., the data segment number, are in thisaddress space. Segments may also contain metadata, which enable dataredundancy to be restored (rewritten to different flash locations ordevices) without the involvement of higher level software. In oneembodiment, an internal format of a segment contains client data andmedium mappings to determine the position of that data. Each datasegment is protected, e.g., from memory and other failures, by breakingthe segment into a number of data and parity shards, where applicable.The data and parity shards are distributed, i.e., striped, acrossnon-volatile solid state storage 152 coupled to the host CPUs 156 (SeeFIG. 5) in accordance with an erasure coding scheme. Usage of the termsegments refers to the container and its place in the address space ofsegments in some embodiments. Usage of the term stripe refers to thesame set of shards as a segment and includes how the shards aredistributed along with redundancy or parity information in accordancewith some embodiments.

A series of address-space transformations takes place across an entirestorage system. At the top are the directory entries (file names) whichlink to an inode. Inodes point into medium address space, where data islogically stored. Medium addresses may be mapped through a series ofindirect mediums to spread the load of large files, or implement dataservices like deduplication or snapshots. Medium addresses may be mappedthrough a series of indirect mediums to spread the load of large files,or implement data services like deduplication or snapshots. Segmentaddresses are then translated into physical flash locations. Physicalflash locations have an address range bounded by the amount of flash inthe system in accordance with some embodiments. Medium addresses andsegment addresses are logical containers, and in some embodiments use a128 bit or larger identifier so as to be practically infinite, with alikelihood of reuse calculated as longer than the expected life of thesystem. Addresses from logical containers are allocated in ahierarchical fashion in some embodiments. Initially, each non-volatilesolid state storage 152 may be assigned a range of address space. Withinthis assigned range, the non-volatile solid state storage 152 is able toallocate addresses without synchronization with other non-volatile solidstate storage 152.

Data and metadata is stored by a set of underlying storage layouts thatare optimized for varying workload patterns and storage devices. Theselayouts incorporate multiple redundancy schemes, compression formats andindex algorithms. Some of these layouts store information aboutauthorities and authority masters, while others store file metadata andfile data. The redundancy schemes include error correction codes thattolerate corrupted bits within a single storage device (such as a NANDflash chip), erasure codes that tolerate the failure of multiple storagenodes, and replication schemes that tolerate data center or regionalfailures. In some embodiments, low density parity check (LDPC) code isused within a single storage unit. Reed-Solomon encoding is used withina storage cluster, and mirroring is used within a storage grid in someembodiments. Metadata may be stored using an ordered log structuredindex (such as a Log Structured Merge Tree), and large data may not bestored in a log structured layout.

In order to maintain consistency across multiple copies of an entity,the storage nodes agree implicitly on two things through calculations:(1) the authority that contains the entity, and (2) the storage nodethat contains the authority. The assignment of entities to authoritiescan be done by pseudorandomly assigning entities to authorities, bysplitting entities into ranges based upon an externally produced key, orby placing a single entity into each authority. Examples of pseudorandomschemes are linear hashing and the Replication Under Scalable Hashing(RUSH) family of hashes, including Controlled Replication Under ScalableHashing (CRUSH). In some embodiments, pseudo-random assignment isutilized only for assigning authorities to nodes because the set ofnodes can change. The set of authorities cannot change so any subjectivefunction may be applied in these embodiments. Some placement schemesautomatically place authorities on storage nodes, while other placementschemes rely on an explicit mapping of authorities to storage nodes. Insome embodiments, a pseudorandom scheme is utilized to map from eachauthority to a set of candidate authority owners. A pseudorandom datadistribution function related to CRUSH may assign authorities to storagenodes and create a list of where the authorities are assigned. Eachstorage node has a copy of the pseudorandom data distribution function,and can arrive at the same calculation for distributing, and laterfinding or locating an authority. Each of the pseudorandom schemesrequires the reachable set of storage nodes as input in some embodimentsin order to conclude the same target nodes. Once an entity has beenplaced in an authority, the entity may be stored on physical devices sothat no expected failure will lead to unexpected data loss. In someembodiments, rebalancing algorithms attempt to store the copies of allentities within an authority in the same layout and on the same set ofmachines.

Examples of expected failures include device failures, stolen machines,datacenter fires, and regional disasters, such as nuclear or geologicalevents. Different failures lead to different levels of acceptable dataloss. In some embodiments, a stolen storage node impacts neither thesecurity nor the reliability of the system, while depending on systemconfiguration, a regional event could lead to no loss of data, a fewseconds or minutes of lost updates, or even complete data loss.

In the embodiments, the placement of data for storage redundancy isindependent of the placement of authorities for data consistency. Insome embodiments, storage nodes that contain authorities do not containany persistent storage. Instead, the storage nodes are connected tonon-volatile solid state storage units that do not contain authorities.The communications interconnect between storage nodes and non-volatilesolid state storage units consists of multiple communicationtechnologies and has non-uniform performance and fault tolerancecharacteristics. In some embodiments, as mentioned above, non-volatilesolid state storage units are connected to storage nodes via PCIexpress, storage nodes are connected together within a single chassisusing Ethernet backplane, and chassis are connected together to form astorage cluster. Storage clusters are connected to clients usingEthernet or fiber channel in some embodiments. If multiple storageclusters are configured into a storage grid, the multiple storageclusters are connected using the Internet or other long-distancenetworking links, such as a “metro scale” link or private link that doesnot traverse the internet.

Authority owners have the exclusive right to modify entities, to migrateentities from one non-volatile solid state storage unit to anothernon-volatile solid state storage unit, and to add and remove copies ofentities. This allows for maintaining the redundancy of the underlyingdata. When an authority owner fails, is going to be decommissioned, oris overloaded, the authority is transferred to a new storage node.Transient failures make it non-trivial to ensure that all non-faultymachines agree upon the new authority location. The ambiguity thatarises due to transient failures can be achieved automatically by aconsensus protocol such as Paxos, hot-warm failover schemes, via manualintervention by a remote system administrator, or by a local hardwareadministrator (such as by physically removing the failed machine fromthe cluster, or pressing a button on the failed machine). In someembodiments, a consensus protocol is used, and failover is automatic. Iftoo many failures or replication events occur in too short a timeperiod, the system goes into a self-preservation mode and haltsreplication and data movement activities until an administratorintervenes in accordance with some embodiments.

As authorities are transferred between storage nodes and authorityowners update entities in their authorities, the system transfersmessages between the storage nodes and non-volatile solid state storageunits. With regard to persistent messages, messages that have differentpurposes are of different types. Depending on the type of the message,the system maintains different ordering and durability guarantees. Asthe persistent messages are being processed, the messages aretemporarily stored in multiple durable and non-durable storage hardwaretechnologies. In some embodiments, messages are stored in RAM, NVRAM andon NAND flash devices, and a variety of protocols are used in order tomake efficient use of each storage medium. Latency-sensitive clientrequests may be persisted in replicated NVRAM, and then later NAND,while background rebalancing operations are persisted directly to NAND.

Persistent messages are persistently stored prior to being transmitted.This allows the system to continue to serve client requests despitefailures and component replacement. Although many hardware componentscontain unique identifiers that are visible to system administrators,manufacturer, hardware supply chain and ongoing monitoring qualitycontrol infrastructure, applications running on top of theinfrastructure address virtualize addresses. These virtualized addressesdo not change over the lifetime of the storage system, regardless ofcomponent failures and replacements. This allows each component of thestorage system to be replaced over time without reconfiguration ordisruptions of client request processing.

In some embodiments, the virtualized addresses are stored withsufficient redundancy. A continuous monitoring system correlateshardware and software status and the hardware identifiers. This allowsdetection and prediction of failures due to faulty components andmanufacturing details. The monitoring system also enables the proactivetransfer of authorities and entities away from impacted devices beforefailure occurs by removing the component from the critical path in someembodiments.

FIG. 3 is a multiple level block diagram, showing contents of a storagenode 150 and contents of a non-volatile solid state storage 152 of thestorage node 150. Data is communicated to and from the storage node 150by a network interface controller (NIC) 202 in some embodiments. Eachstorage node 150 has a CPU 156, and one or more non-volatile solid statestorage 152, as discussed above. Moving down one level in FIG. 3, eachnon-volatile solid state storage 152 has a relatively fast non-volatilesolid state memory, such as nonvolatile random access memory (NVRAM)204, and flash memory 206. In some embodiments, NVRAM 204 may be acomponent that does not require program/erase cycles (DRAM, MRAM, PCM),and can be a memory that can support being written vastly more oftenthan the memory is read from. Moving down another level in FIG. 3, theNVRAM 204 is implemented in one embodiment as high speed volatilememory, such as dynamic random access memory (DRAM) 216, backed up byenergy reserve 218. Energy reserve 218 provides sufficient electricalpower to keep the DRAM 216 powered long enough for contents to betransferred to the flash memory 206 in the event of power failure. Insome embodiments, energy reserve 218 is a capacitor, super-capacitor,battery, or other device, that supplies a suitable supply of energysufficient to enable the transfer of the contents of DRAM 216 to astable storage medium in the case of power loss. The flash memory 206 isimplemented as multiple flash dies 222, which may be referred to aspackages of flash dies 222 or an array of flash dies 222. It should beappreciated that the flash dies 222 could be packaged in any number ofways, with a single die per package, multiple dies per package (i.e.multichip packages), in hybrid packages, as bare dies on a printedcircuit board or other substrate, as encapsulated dies, etc. In theembodiment shown, the non-volatile solid state storage 152 has acontroller 212 or other processor, and an input output (I/O) port 210coupled to the controller 212. I/O port 210 is coupled to the CPU 156and/or the network interface controller 202 of the flash storage node150. Flash input output (I/O) port 220 is coupled to the flash dies 222,and a direct memory access unit (DMA) 214 is coupled to the controller212, the DRAM 216 and the flash dies 222. In the embodiment shown, theI/O port 210, controller 212, DMA unit 214 and flash I/O port 220 areimplemented on a programmable logic device (PLD) 208, e.g., a fieldprogrammable gate array (FPGA). In this embodiment, each flash die 222has pages, organized as sixteen kB (kilobyte) pages 224, and a register226 through which data can be written to or read from the flash die 222.In further embodiments, other types of solid-state memory are used inplace of, or in addition to flash memory illustrated within flash die222.

Storage cluster 160, in various embodiments as disclosed herein, can becontrasted with storage arrays in general. The storage nodes 150 arepart of a collection that creates the storage cluster 160. Each storagenode 150 owns a slice of data and computing required to provide thedata. Multiple storage nodes 150 cooperate to store and retrieve thedata. Storage memory or storage devices, as used in storage arrays ingeneral, are less involved with processing and manipulating the data.Storage memory or storage devices in a storage array receive commands toread, write, or erase data. The storage memory or storage devices in astorage array are not aware of a larger system in which they areembedded, or what the data means. Storage memory or storage devices instorage arrays can include various types of storage memory, such as RAM,solid state drives, hard disk drives, etc. The storage units 152described herein have multiple interfaces active simultaneously andserving multiple purposes. In some embodiments, some of thefunctionality of a storage node 150 is shifted into a storage unit 152,transforming the storage unit 152 into a combination of storage unit 152and storage node 150. Placing computing (relative to storage data) intothe storage unit 152 places this computing closer to the data itself.The various system embodiments have a hierarchy of storage node layerswith different capabilities. By contrast, in a storage array, acontroller owns and knows everything about all of the data that thecontroller manages in a shelf or storage devices. In a storage cluster160, as described herein, multiple controllers in multiple storage units152 and/or storage nodes 150 cooperate in various ways (e.g., forerasure coding, data sharding, metadata communication and redundancy,storage capacity expansion or contraction, data recovery, and so on).

FIG. 4A depicts a file 402, suitable for storage and access inembodiments of the storage cluster 160, with file chunks 406 each havinga file offset 404 relative to the file 402. The file 402 is identifiedby an inode number 410, for example as a file system object. Directoriesmay also be identified by inode numbers, in some embodiments. The fileoffset 404 of a specific file chunk 406 is the address of the beginningof the file chunk 406 relative to the beginning of the file 402 in thisexample, although other definitions for offsets could be used. A file402 of a given file size 408 could have few or many file chunks 406,which could be various sizes. For example, a file chunk 406 could be anumber of kilobytes, a number of megabytes, a number of gigabytes, orconceivably a number of terabytes, etc. In typical, known storagesystems, ownership of all of the file chunks 406 for a specific file, oreven all of the file chunks 406 for all files in the system, is found inone location in the storage system, such as in a storage node. Thiscreates a bottleneck, especially for large files, which ties up systemresources and inhibits throughput. By contrast, ownership of file chunks406 is distributed throughout storage nodes 150 in present embodimentsof the storage cluster 160. This more evenly distributes or partitionssystem resource load across a file.

FIG. 4B shows an example file 402, and ownership of various file chunks406 of the file 402, in accordance with an embodiment of the presentdescription. In this example, the file 402 has a file size 408 of 1 TB(terabyte), and chunk size of 16 kB (kilobytes) although other filesizes 408 and sizes for file chunks 406 could be used. The file 402 isidentified by “inode 65” as the inode number 410. File chunks 406 areowned by various authorities 168. For example, the first file chunk 406in the example is shown as owned by an authority 168 identified as“authority 42”, the second file chunk 406 is shown as owned by anauthority 168 identified as “authority 50”, and the third file chunk 406is shown as owned by an authority 168 identified as “authority 40”. Itis likely most file chunks 406 of the file 402 are owned by differentauthorities 168, but it is statistically possible and indeed in verylarge files, statistically likely, that two or more file chunks 406could be owned by the same authority 168. It should be appreciated thatthis statistical likelihood depends upon the total number of authorities168 in the storage cluster 160 as compared to the total number of filechunks 406 in the file 402.

FIG. 5 is a block diagram of a storage cluster 160 with components fordetermining ownership of file chunks 406. In some embodiments, eachstorage node 150 of the storage cluster 160 has one or more authorities168, a hash calculator 502, and storage memory 506, although fewer thanall of the storage nodes 150 could have these components, with somestorage nodes 150 as compute nodes. User data is stored in storagememory 506 of the storage nodes 150, for example using erasure codingand distribution in accordance with authorities 168 as described abovewith reference to FIGS. 1-3. Operation of the hash calculator 502 isdescribed below with reference to FIG. 6. The hash calculator 502 couldbe implemented in firmware, hardware, or software executing on aprocessor, or combinations thereof. Operation of the hash calculator 502could be performed by a processor 156 of a storage node 150 (see FIG.2). It should be appreciated that storage nodes 150 could include one ormore logical constructs of a compute agent holding storage information,and/or one or more logical constructs of a compute agent configured toservice a client request, in a storage system.

FIG. 6 is a system action diagram showing use of a hash calculator 502that identifies an authority 168 as an owner of a file chunk 406. Theinode number 410, as an identifier of a file 402, and the file offset404 of a file chunk 406 relative to the file 402, are fed into the hashcalculator 502, which produces a hash calculation result 602. This couldbe implemented by having a processor 156 of a storage node 150 perform ahash calculation on the file identifier and the offset 404. The hashcalculation result 602 identifies an authority 168. The messaging systemof the storage system enables communication to the authority identifiedby the hash calculation result. Mode numbers 410 or other fileidentifiers, file offsets 404 or other information about file chunks406, file sizes 408, and information handled by authorities 168 relatingto files 402, file chunks 406, directories, etc., may be referred to astypes of metadata. FIGS. 4A-6 thus describe a mechanism for delegatingthe location of portions of metadata for files, which can also be usedfor various further objects. It should be appreciated that some storagenodes of the system may not include an authority in some embodiments asa portion or subset of the storage nodes may include an authority, asopposed to each storage node including an authority in otherembodiments.

FIG. 7A is a flow diagram of a method for distributing ownership of filechunks in a storage system, and writing file chunks of files, which canbe practiced by embodiments of the storage cluster, storage nodes andstorage units of FIGS. 1-6. The method can be practiced by one or moreprocessors in a storage system. In an action 702, a request is receivedto write a file to storage memory. The request could be received by astorage node. In an action 704, the file is portioned or segmented intofile chunks. In an action 706, for each file chunk of the file, a hashcalculation is performed on the file offset of the file chunk and a fileidentifier, e.g., an inode number of the file. In an action 708, foreach file chunk the authority is identified based on the hashcalculation result for that file chunk. In an action 710, the authoritydirects storage of the file chunk. The file chunks are stored inaccordance with direction by the associated authorities, in an action712.

FIG. 7B is a flow diagram of a method for distributing ownership of filechunks in a storage system, and accessing file chunks of files, whichcan be practiced by embodiments of the storage cluster, storage nodesand storage units of FIGS. 1-6. The method can be practiced by one ormore processors in a storage system. In an action 714, a request isreceived to read a file from storage memory. The request could bereceived by a storage node. In an action 716, an authority is determinedor identified among differing storage nodes of the storage system foreach file chunk of the file. In some embodiments, a hash calculation isperformed on the file offset of the file chunk and a file identifier,e.g., an inode number of the file, for each file chunk of the file. Inan action 718, location information for the file chunk for each filechunk is received from the authority having ownership of the file chunk.In an action 720, the file chunks of the file are accessed as directedby each of the determined authorities. It should be appreciated that theembodiments determine one of a plurality of owners in a plurality ofstorage nodes as having ownership of a file chunk of the file, and thedetermining is performed at differing storage nodes for each of aplurality of file chunks of the file. Thus, the distribution ofownership of chunks of a file enables the efficient access to those filechunks without the need of a centralized look up table or agent tomanage the process. That is, differing authorities distributed amongdiffering storage nodes have ownership for various chunks or portions ofa file according to the mechanisms described above.

It should be appreciated that the methods described herein may beperformed with a digital processing system, such as a conventional,general-purpose computer system. Special purpose computers, which aredesigned or programmed to perform only one function may be used in thealternative. FIG. 8 is an illustration showing an exemplary computingdevice which may implement the embodiments described herein. Thecomputing device of FIG. 8 may be used to perform embodiments of thefunctionality for distributing ownership of file chunks in a storagesystem in accordance with some embodiments. The computing deviceincludes a central processing unit (CPU) 801, which is coupled through abus 805 to a memory 803, and mass storage device 807. Mass storagedevice 807 represents a persistent data storage device such as a discdrive, which may be local or remote in some embodiments. The massstorage device 807 could implement a backup storage, in someembodiments. Memory 803 may include read only memory, random accessmemory, etc. Applications resident on the computing device may be storedon or accessed via a computer readable medium such as memory 803 or massstorage device 807 in some embodiments.

Applications may also be in the form of modulated electronic signalsmodulated accessed via a network modem or other network interface of thecomputing device. It should be appreciated that CPU 801 may be embodiedin a general-purpose processor, a special purpose processor, or aspecially programmed logic device in some embodiments.

Display 811 is in communication with CPU 801, memory 803, and massstorage device 807, through bus 805. Display 811 is configured todisplay any visualization tools or reports associated with the systemdescribed herein. Input/output device 809 is coupled to bus 805 in orderto communicate information in command selections to CPU 801. It shouldbe appreciated that data to and from external devices may becommunicated through the input/output device 809. CPU 801 can be definedto execute the functionality described herein to enable thefunctionality described with reference to FIGS. 1-7B. The code embodyingthis functionality may be stored within memory 803 or mass storagedevice 807 for execution by a processor such as CPU 801 in someembodiments. The operating system on the computing device may beMS-WINDOWS™, UNIX™, LINUX™, iOS™, CentOS™, Android™, Redhat Linux™,z/OS™, or other known operating systems. It should be appreciated thatthe embodiments described herein may also be integrated with avirtualized computing system implemented with physical computingresources.

Detailed illustrative embodiments are disclosed herein. However,specific functional details disclosed herein are merely representativefor purposes of describing embodiments. Embodiments may, however, beembodied in many alternate forms and should not be construed as limitedto only the embodiments set forth herein. It should be appreciated thatwhile the embodiments are described with respect to file systems, theembodiments may be extended to object based systems also.

It should be understood that although the terms first, second, etc. maybe used herein to describe various steps or calculations, these steps orcalculations should not be limited by these terms. These terms are onlyused to distinguish one step or calculation from another. For example, afirst calculation could be termed a second calculation, and, similarly,a second step could be termed a first step, without departing from thescope of this disclosure. As used herein, the term “and/or” and the “/”symbol includes any and all combinations of one or more of theassociated listed items.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising”, “includes”, and/or “including”, when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. Therefore, the terminology usedherein is for the purpose of describing particular embodiments only andis not intended to be limiting.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

With the above embodiments in mind, it should be understood that theembodiments might employ various computer-implemented operationsinvolving data stored in computer systems. These operations are thoserequiring physical manipulation of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated. Further, the manipulationsperformed are often referred to in terms, such as producing,identifying, determining, or comparing. Any of the operations describedherein that form part of the embodiments are useful machine operations.The embodiments also relate to a device or an apparatus for performingthese operations. The apparatus can be specially constructed for therequired purpose, or the apparatus can be a general-purpose computerselectively activated or configured by a computer program stored in thecomputer. In particular, various general-purpose machines can be usedwith computer programs written in accordance with the teachings herein,or it may be more convenient to construct a more specialized apparatusto perform the required operations.

A module, an application, a layer, an agent or other method-operableentity could be implemented as hardware, firmware, or a processorexecuting software, or combinations thereof. It should be appreciatedthat, where a software-based embodiment is disclosed herein, thesoftware can be embodied in a physical machine such as a controller. Forexample, a controller could include a first module and a second module.A controller could be configured to perform various actions, e.g., of amethod, an application, a layer or an agent.

The embodiments can also be embodied as computer readable code on anon-transitory computer readable medium. The computer readable medium isany data storage device that can store data, which can be thereafterread by a computer system. Examples of the computer readable mediuminclude hard drives, network attached storage (NAS), read-only memory,random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and otheroptical and non-optical data storage devices. The computer readablemedium can also be distributed over a network coupled computer system sothat the computer readable code is stored and executed in a distributedfashion. Embodiments described herein may be practiced with variouscomputer system configurations including hand-held devices, tablets,microprocessor systems, microprocessor-based or programmable consumerelectronics, minicomputers, mainframe computers and the like. Theembodiments can also be practiced in distributed computing environmentswhere tasks are performed by remote processing devices that are linkedthrough a wire-based or wireless network.

Although the method operations were described in a specific order, itshould be understood that other operations may be performed in betweendescribed operations, described operations may be adjusted so that theyoccur at slightly different times or the described operations may bedistributed in a system which allows the occurrence of the processingoperations at various intervals associated with the processing.

In various embodiments, one or more portions of the methods andmechanisms described herein may form part of a cloud-computingenvironment. In such embodiments, resources may be provided over theInternet as services according to one or more various models. Suchmodels may include Infrastructure as a Service (IaaS), Platform as aService (PaaS), and Software as a Service (SaaS). In IaaS, computerinfrastructure is delivered as a service. In such a case, the computingequipment is generally owned and operated by the service provider. Inthe PaaS model, software tools and underlying equipment used bydevelopers to develop software solutions may be provided as a serviceand hosted by the service provider. SaaS typically includes a serviceprovider licensing software as a service on demand. The service providermay host the software, or may deploy the software to a customer for agiven period of time. Numerous combinations of the above models arepossible and are contemplated.

Various units, circuits, or other components may be described or claimedas “configured to” perform a task or tasks. In such contexts, the phrase“configured to” is used to connote structure by indicating that theunits/circuits/components include structure (e.g., circuitry) thatperforms the task or tasks during operation. As such, theunit/circuit/component can be said to be configured to perform the taskeven when the specified unit/circuit/component is not currentlyoperational (e.g., is not on). The units/circuits/components used withthe “configured to” language include hardware—for example, circuits,memory storing program instructions executable to implement theoperation, etc. Reciting that a unit/circuit/component is “configuredto” perform one or more tasks is expressly intended not to invoke 35U.S.C. 112, sixth paragraph, for that unit/circuit/component.Additionally, “configured to” can include generic structure (e.g.,generic circuitry) that is manipulated by software and/or firmware(e.g., an FPGA or a general-purpose processor executing software) tooperate in manner that is capable of performing the task(s) at issue.“Configured to” may also include adapting a manufacturing process (e.g.,a semiconductor fabrication facility) to fabricate devices (e.g.,integrated circuits) that are adapted to implement or perform one ormore tasks.

The foregoing description, for the purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the embodiments and its practical applications, to therebyenable others skilled in the art to best utilize the embodiments andvarious modifications as may be suited to the particular usecontemplated. Accordingly, the present embodiments are to be consideredas illustrative and not restrictive, and the invention is not to belimited to the details given herein, but may be modified within thescope and equivalents of the appended claims.

What is claimed is:
 1. A method, comprising: determining for each filechunk of a file, ownership of each file chunk based on metadata of acorresponding file chunk, wherein ownership of file chunks of the fileis distributed across storage nodes of a storage system; receiving, fromthe owner of the file chunk, location information for the file chunk;and accessing file chunks of the file as directed by each of thedetermined owners, wherein the determining, the receiving and theaccessing are executed through a processor of the storage system.
 2. Themethod of claim 1, wherein the determining includes performing a hashcalculation on an identifier of the file and an offset of the filechunk.
 3. The method of claim 1, wherein each storage node includesmultiple owners.
 4. The method of claim 1, wherein differing ones of theplurality of storage nodes of the storage system contain differingowners for differing file chunks of the file.
 5. The method of claim 1,wherein the metadata includes an inode number of the file and an offsetof the file chunk.
 6. The method of claim 1, wherein the ownershipdistributed across the storage nodes directs data recovery in case offailure of a storage node.
 7. The method of claim 1, wherein thedetermining for each file chunk is not centralized in the storagesystem.
 8. A method, comprising: determining one of a plurality ofowners as having ownership of a file chunk of a file, the determiningperformed at differing storage nodes for each of a plurality of filechunks of the file, with file chunks of the file distributed across theplurality of storage nodes and wherein the determining includesperforming a hash calculation on metadata associated with correspondingfile chunk; and accessing the plurality of file chunks of the file asdirected by determined owners, wherein the determining and the accessingare executed through a processor of a storage system.
 9. The method ofclaim 8, wherein each storage node includes multiple owners.
 10. Themethod of claim 8, wherein the determining comprises: performing thehash calculation on a file offset for the file chunk and on an inodenumber of the file, wherein a result of the hash calculation identifiesone of the plurality of owners as having the ownership of the filechunk.
 11. The method of claim 8 wherein the metadata includes anidentifier of the file and an offset of the file chunk.
 12. The methodof claim 8, the determining is not centralized in the storage system.13. The method of claim 8, wherein the plurality of owners direct datarecovery in case of failure of a storage node.
 14. A storage system,comprising: a plurality of storage nodes coupled as a storage cluster;at least a portion of the plurality of storage nodes configured to haveat least one owner having ownership of a subset of file chunks of a fileand associated with determining how and where each file chunk of thesubset of file chunks is stored in the storage system and the subset offile chunks is distributed across the storage nodes; and each of theplurality of storage nodes configured to perform a hash calculationbased on a metadata associated with corresponding file chunk, wherein aresult of the hash calculation indicates location information for thefile chunk.
 15. The system of claim 14, wherein each owner directs datarecovery in case of failure of a storage node.
 16. The system of claim14, further comprising: each of the plurality of storage nodesconfigured to apply a result of the hash calculation to a lookup table,to determine an owner having the location information.
 17. The system ofclaim 14, wherein the result of the hash calculation indicates one ofthe plurality of storage nodes having the owner.
 18. The system of claim14, wherein the metadata includes an inode number of the file and anoffset of the file chunk.
 19. The system of claim 14, wherein each ofthe plurality of storage nodes including a logical construct of acompute agent holding storage information.
 20. The system of claim 14,wherein each storage node of the plurality of storage nodes includesflash memory and wherein each storage node includes multiple owners.